Metal alloy composition



United States Patent Office 3,424,577 Patented Jan. 28, 1969 ABSTRACT OFTHE DISCLOSURE A non-tarnishing gold alloy by weight consists of 50- 60%silver and copper; at least 3-6% palladium; and the balance gold. Thepalladium serves to minimize the tarnishing of the silver content of thealloy.

This invention relates to alloys and more particularly to alloy-s whichinclude copper and silver as essential constituent metals in preciousmetal alloys, especially for use in cast or wrought dental work and forthe manufacture of articles of jewelry, and industrial items such aselectrical contacts.

Heretofore, the tarnishing of gold alloys and other alloys of a preciousmetal color was attributed to and was believed to be caused by thecopper content of such alloys.

We have discovered that, contrary to prior belief, tarnishing of alloysof the above mentioned character results from the silver content and byreason of this discovery We have succeeded in the objective of ourinvention which is to provide an alloy of gold color or of otherprecious metal color which is non-tarnishing, or highly resistant totarnishing, and which can be produced at decreased cost.

In accordance with our invention a non-tarnishing alloy of gold color isobtainable when the combined copper and silver content constitutes 55%of the alloy composition and when there is present at least 5% or more,preferably, 6% of palladium, the rest of the composition being goldwhich constitutes 40% of the composition when 5% of the composition ispalladium and which constitutes 39% of the composition when thepalladium content is 6%. We have found that at least 5% of palladium inthe alloy having a combined copper and silver content of 55% isnecessary to prevent an intolerable tarnishing of the gold color andthat 6% of palladium or more in the alloy.

The ratio of silver to copper in the above mentioned combined silver andcopper content of 55% is preferably 3 of silver to 2 of copper. Withthis ratio of silver to copper and with a gold content of 39%, the alloyhas a pleasing color of light-yellow gold. If an alloy having a lightcolor is desired, the percentage of palladium is increased correspondingto the decrease in the amount of gold. For example, when the combinedcopper and silver content is 60% and the palladium content is 6%, thegold content being 34%, the color of the gold alloy will be that ofwhite gold.

Limited variations in the silver to copper ratio in the combined silverand copper content of 55% are permissible, for example, for 3 silver to2 copper to reversed ratios ranging from 3 copper to 2 silver. However,the amount of palladium remains as above indicated, namely not less than5%, even when the ratio of silver to copper is 2:3.

The preferred composition of the alloy of gold color is:

A reduction in the combined silver and copper content of an alloy ofgold color to 50% is within the scope of this invention, the ratio ofsilver to copper varying from 3 silver to 2 copper to 2 silver to 3copper as in the above combined silver and copper content of 55 Withsuch content of silver and copper, the minimum permissible quantity ofpalladium to prevent tarnishing is 3%, the maximum gold content being47%. The following is a preferred composition when the combined silverand gogper content is 50% and the silver to copper ratio is Palladium 4Gold 46 Silver 30 Copper 20 As used in certain of the claims,hereinafter appended, the term precious metal is applicable to gold,palladium and platinum.

While we have shown and described the preferred embodiments of ourinvention, it will be understood that the invention may be embodiedotherwise than as herein specifically illustrated or described, and thatcertain changes in the form and arrangement of parts and in the specificmanner of practicing the invention may be made without departing fromthe underlying idea or principles of this invention within the scope ofthe appended claims.

What is claimed is:

1. A non-tarnishing metal alloy having a color of one of the groupconsisting of yellow, white and combinations thereof, consisting of 50to 60 percent silver plus copper, 3 to 6 percent palladium and thebalance gold, wherein the silver to copper content in weight percentvaries from 3 to 2 through 2 to 3, and further characterized by havingat 50 percent silver plus copper content a minimum palladium content of3 percent and at 60 percent silver plus copper content a minimumpalladium content of 5 percent and at 60 percent silver plus coppercontent a minimum palladium content of 6 percent.

2. A metal alloy as defined by claim 1, wherein the combined silver andcopper content is 55%, the palladium content is 6% and gold in theamount of 39% 3. A metal alloy as defined by claim 1, wherein thecombined silver and copper content is 50%, the palladium content is 4%and gold in the amount of 46% 4. A metal alloy as defined by claim 1,containing gold in the amount of from about 39% to about 47%.

5. A metal alloy according to claim 1, wherein the combined silver andcopper content is 60 percent, the palladium content is 6 percent andgold in the amount of 34 percent.

References Cited UNITED STATES PATENTS 1,913,423 6/1933 Wise -1721,935,897 11/1933 Wise 75-172 1,987,451 1/1935 Taylor 75--73 2,050,0408/1936 Coleman 75134 2,050,077 8/ 1936 Wise 75-134- FOREIGN PATENTS354,239 7/ 1931 Great Britain.

OTHER REFERENCES Transactions of AIMME, -vol. 99, 1932, pp. 380-387 and399-406 relied on.

CHARLES N. LOVELL, Primary Examiner.

US. Cl. X.R. 75122 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTIONPatent No. 3,424,577 January 28, 1969 John P. Nielsen et a1.

It is certified that error appears in the above identified patent andthat said Letters Patent are hereby corrected as shown below:

Column 2, line 36, "60" should read 55 Signed and sealed this 7th day ofApril 1970.

(SEAL) Attest:

Attesting Officer WILLIAM E. SCHUYLER, JR.

